The present invention relates to tubular lost borehole closures, especially for injection of plastic material or the like into a borehole for consolidation of rock, and essentially comprising a tube provided with a return flow guard, a holding element and a sealing element, in which a spanning element in form of a screw nipple serves to span the sealing and holding elements.
Such a tubular lost borehole closure for injection of plastic material is known in the art and for instance disclosed in the German Pat. No. 25 50 555. This known tubular lost borehole closure comprises a tube forming a throttle passage and surrounded by a hose section consisting of elastic material and serving only as a sealing element which at opposite ends is provided with sliding discs by means of which it is guided on the tube. This known lost borehole closure comprises further a holding element including a spreading cone threadingly connected to a portion of the tube and cooperating with a spreadable bushing and an abutment disc likewise threadingly connected to the tube. A spanning element in form of a screw nipple which is screwed onto another portion of the tube serves to span the sealing element and the holding element.
A disadvantage of this known lost borehole closure is that it can only be applied in the region of the outer end of the borehole, that it does not have a sufficient return flow guard and that the mixing of the material to be injected has to be carried out outside of this known borehole closure.
This known lost borehole closure has already been further developed by providing at the leading end thereof a return flow guard comprising a spring biased ball valve arranged in a housing provided at the axis of the tube with an opening at the front of the housing.
However, despite this improvement of the known lost borehole closure it has still the decisive disadvantage that it may not be used at any position of the borehole. In addition, the above-mentioned return flow guard has certain disadvantages, especially that, when the spring is compressed by the pressure of the medium to be injected, the throughflow of the injected medium will not be assured.